Polarizing ophthalmic devices, such as polarizing sunglasses, can reduce glare due to light reflected off surfaces, such as but not limited to pavement, water, and snow, thereby enhancing vision under glare conditions. Consequently, polarizing ophthalmic devices have become of increasing interest for use in sports and other outdoor activities in which reflected glare can be problematic.
Conventional polarizing filters for ophthalmic devices are formed from sheets or layers of a polymeric material that has been stretched or otherwise oriented and impregnated with an iodine, chromophore or dichroic dye. For example, one method of forming a conventional polarizing filter for ophthalmic devices is to heat a sheet or layer of polyvinyl alcohol (“PVA”) to soften the PVA and then stretch the sheet to orient the PVA polymer chains. Thereafter, an iodine chromophore or dichroic dye is impregnated into the sheet such that the iodine or dye molecules attach to the aligned polymer chains and take on a particular order or alignment. Alternatively, the iodine chromophore or the dichroic dye can be first impregnated into the PVA sheet, and thereafter the sheet can be heated and stretched as described above to orient the PVA polymer chains and associated chromophore or dye.
Iodine chromophores and dichroic dyes are dichroic materials, that is, they absorb one of two orthogonal plane-polarized components of transmitted radiation more strongly than the other. Although dichroic materials will preferentially absorb one of two orthogonal plane-polarized components of transmitted radiation, if the molecules of the dichroic material are not suitably positioned or arranged, no net polarization of transmitted radiation will be achieved. That is, due to the random positioning of the molecules of the dichroic material, the selective absorption by the individual molecules will cancel each other such that no net or overall polarizing effect is achieved. However, by suitably positioning or arranging the molecules of the dichroic material within the oriented polymer chains of the PVA sheet, a net polarization can be achieved. That is, the PVA sheet can be made to polarize transmitted radiation, or in other words, a polarizing filter can be formed. As used herein, the term “polarize” means to confine the vibrations of the electric vector of light waves to one direction.
One method of forming a polarizing ophthalmic device utilizing such polarizing polymer sheet filters is to laminate or glue the filter to the convex outer surface of a lens substrate. Another method of forming lenses utilizing conventional polarizing polymer sheet filters involves lining the surface of a lens mold with the polarizing sheet and subsequently filling the mold with the substrate material such that the polarizing sheet is on the surface of the lens when removed from the mold. Still other methods involve the incorporation of the filter into the lens structure itself. For example, the filter can be incorporated into the lens structure by laminating the filter between two substrates that together form the lens, or by casting a substrate material around the filter. In the latter method, the polarizing filter can be placed into a mold and the mold filled with the substrate material, typically a thermosetting plastic monomer, such that the substrate material surrounds and encapsulates the polarizing filter. Thereafter, the substrate material can be cured to form the lens.
It is also known to form a polarizing layer by forming a film of a linear photo-polymerizable material exhibiting selective orientation on a release layer component of a transfer foil. Thereafter, a liquid crystal polymer material containing a dichroic dye can be applied to the linear photo-polymerizable material and the chains of the liquid crystal polymer aligned. Since a dichroic dye is contained within the liquid crystal polymer, when the liquid crystal polymer chains are aligned, the dichroic dye molecules are also aligned and a net polarization effect can be achieved. The polarizing layer can then be transferred from the transfer foil to a suitable substrate by, for example, hot stamping.
Other methods of forming polarizing sheets or layers using liquid crystal materials are also known. For example, polarizing sheets formed from oriented thermotropic liquid crystal films containing dichroic dyes have been disclosed. Further, polarizing sheets formed by extruding liquid crystalline polymers that contain dichroic dyes covalently linked as part of the main polymer chains have been disclosed.